This whole mess started with trying to encrypt Time Machine backups. I have a 4TB Lacie P9230 external drive which has been working for about a year just fine. The drive has been partitioned into two partitions, one for TM backups and other as archive and other stuff that isn't important or can be downloaded from the internet. When I tried to enable Time Machine encryption, the process failed and the backup partition disappeared. Disk Utility listed it as grey and couldn't mount it or something. Then I did the wisest thing and simply unplugged the drive's power cord and reconnected. Now it's in this weird state where the volume apparently doesn't have a file system nor does the backup partition. The archive partition has a file system (JHFS+) and it is visible in Finder, but all the folders are there but they empty even though Disk Utility shows the correct amount of data used. I did try reformatting the whole volume, copying /dev/zero but nothing worked.

At some point in time between my drive disconnect/reconnects, the mdls command returned 0 values for everything. Finder still doesn't show anything in the folder.

I have tried reformatting the volume in Disk Utility, but it either cannot unmount it or cannot write to the last block. I then tried running this sudo dd if=/dev/zero of=/dev/rdisk2 bs=64k which resulted in the following error:

I have ran out of things to try on this drive. I have started to wonder whether the drive itself is starting to fail, but it was working just fine before I started messing around with it. If anyone has a solution that could preserve the data that would be perfect, but I don't really expect that to be even possible. All the data is disposable so if I could just reformat it and get back to using it (unless it is failing).

E1: The archive partition has magically restored some of the data, meaning I can now access data in the drive that was previously missing. Some data is still missing and I don't have a spare drive with sufficient capacity where I could offload the data in case it is failing.

E2: The drive works perfectly when connected to another Mac. It shows that it is encrypting (0%), so I'll let it finish the encryption and reinstall OS X on my main machine so that once the drive is encrypted, I hope it will be detected normally.

1 Answer
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Apparently I was asking the wrong question. After attaching this "corrupted" drive to another Mac, it simply asked for the password and mounted the drives with all their data as normal. I let the other Mac finish the encryption process, reinstalled OS X on my main machine and reconnected the drive and it now works perfectly.